Internal combustion engines such as, for example, gasoline engines, diesel engines, and gaseous fuel powered engines, contain internal moving parts that rely on a pressurized fluid for proper lubrication. The fluid is often a high-viscosity oil, which is introduced between moving parts to create a thin, protective layer of oil, allowing the parts to be separated, thereby reducing friction and wear. A pump draws the fluid from a reservoir and pressurizes it, causing it to flow through passageways in the engine to moving parts that require lubrication. The pressure of the fluid is regulated by a pressure relief valve consisting of a spring-loaded spool, which relieves the fluid pressure by moving the spool against the spring to create a relief passage for the fluid when the pressure reaches a predetermined level.
For a rotating part of an engine that transports oil from its surface to its central axis of rotation, such as, for example, a crank journal that receives oil from an engine block and transports the oil to one or more rod journals, the oil pressure required for proper lubrication increases as the speed of the engine increases. That is, as the rotating speed of moving parts in the engine increases, the pressure required to effectively lubricate moving parts by creating a thin layer of oil between the parts increases. The increase allows the oil to overcome its own inertia to make its way to the center of a crankshaft of the engine. It may be beneficial to operate an engine with the lowest effective oil pressure, to reduce inefficiencies due to pumping losses, and life-reducing heat-cycling of the oil that occurs when dumping high pressure oil to the reservoir through the relief valve. To achieve the lowest effective pressure, the maximum allowable pressure is set to correspond to the required pressure at the maximum operating speed of the engine. Setting the maximum pressure entails adjusting a pre-load force of the spring against the spool in the relief valve.
Due to the location of the pressure regulator on the engine, manually adjusting the maximum allowable oil pressure during operation may not be practical. Though the maximum allowable pressure is generally set to correspond to the pressure required at the maximum operating speed of the engine, modern engines often operate in overspeed conditions that may exceed the maximum engine speed. An overspeed condition of an engine is common on engines that are used in mechanical drive applications. An overspeed condition may result from an operation such as engine braking on a steep grade. Because the engine speed during an overspeed condition may be much higher than at the maximum engine operating speed, the maximum allowable pressure setting of the pressure regulator may not be high enough to provide sufficient lubrication at overspeed conditions, if the maximum pressure was set to correspond to the maximum pressure required at a lower operating speed.
One attempt to vary the oil pressure with the engine speed is described in U.S. Pat. No. 6,488,479 B1 (the '479 patent), issued to Berger on Dec. 3, 2002. The '479 patent discloses a system that includes a variable pressure oil pump. The system also includes a controller (ECU) and various sensors, including an oil pressure sensor, an oil temperature sensor, an engine load sensor, an engine speed sensor, a coolant temperature sensor, and an oil viscosity sensor. The oil pump includes an adjustable pressure regulator that uses a solenoid to move a plunger to selectively allow passage of oil through a bypass when the pressure of the oil is too high. The ECU moves the solenoid to regulate the oil pressure based on inputs from the various sensors, and the ECU may allow a higher maximum oil pressure as the engine speed increases.
Although the system disclosed in the '479 patent may allow a higher maximum oil pressure as engine speeds increase, it may be complex and costly. Specifically, the '479 system requires not only a mechanism to vary the oil pressure, it also requires an ECU and multiple sensors. The additional components increase the control difficulty and expense of the system. The additional components also preclude the retrofit of an oil pressure regulation system on engines that do not include an ECU.
The disclosed pressure regulator is directed to overcoming one or more of the problems set forth above.